Regulators: tps6507x-regulator - mark probe method as __devinit

Also move error handling in probe() out of line and do not bother
to reset fields in structures that are about to be freed.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>